The morphogenesis of copper oxalate polycrystalline pitted and patterned tablets were investigated in a simple precipitation reaction between copper sulfate and oxalic acid solutions. The formation of the pit or pattern on the surfaces of the tablets could be related to an etching or partial dissolution process at the central region of the tablets during aging. The presence of poly(ethylene glycol) (PEG), acidity of the reaction mixture and temperature exhibited significant effect on the morphology of the products, which could be rationally associated with different etching processes under different conditions. (c) 2007 Elsevier B.V. All rights reserved.